Method for the uniform heat treatment of filiform material

ABSTRACT

A method of uniformly heating a filiform material such as filaments, threads, yarn, ribbons or the like which are separately transported through individual heating zones, the filiform material being indirectly heated by means of a recirculated vapor such as saturated steam, the condensate collecting in each of the heating zones being entrained and carried off therefrom by supplying excess vapor to each zone at high vapor velocities and high gas concentrations.

United States Patent Ostertag et al. A i

1541 METHOD FOR THE UNIFORM HEAT TREATMENT OF FILIFORM MATERIAL [72] Inventors: Karl Ostertag, Rosenstr. l8, Elsenfeld;,l-leinrich Nilgens,-Mozartstr. 4,

v Erlenbach, bothofGermany 221 Filed: Feb.'l8,197l 21] Appl.No.: 116,420

52 U.S.Cl ..l65/l, 34/4l 511 lm, c1... ..F26b3/32 [58] FieldofSearch ..165/1, 120; 34/4 77 A [56] References Cited UNITED STATES PATENTS 2,501,979 3/1950 Wood et al. ..34/77 [15] 3,682,238 1 Aug. 8, 1972 2,495,053 1/1950 Conawayetal. ..34/41 3,396,415 8/1968 Meler-Winduorst ..34/41 Primary Examinen-Charles Sukalo Attorney-Johnston, Root, OKeefie, Keil, Thompson & Shurtlefi' v [57] ABSTRACT v A method of uniformly heating a filiform material such as filaments, threads, yarn, ribbons or the like which are separately transported through individual heating zones, the filiform material being indirectly heated by means of a recirculated vapor such as saturated steam, the condensate collecting in each of the heating zones being entrained and carried off therefrom by supplying excess vapor to each zone at high vapor velocities and high gas concentrations.

' 7 (Ilairns, 1 Drawing Figure PATENTEDAUG 8 I972 3 682 238 [.N'VENTORS. 'KARL OSTERTAG HEINRICH NILGENS METHOD FOR THE UNIFORM HEAT TREATMENT OF FILIFORM MATERIAL In the textile or related industries, it is a common practice to subject a filiforrn material to a special heat treatment, for example by transporting a large number of threads, yarns, ribbons or the like over heating plates, pins, godets or similar heating devices while supplying a heat exchange fluid to the heating device, preferably internally of the device in the form of a heating vapor so as to indirectly heat the surfaces in contact with the transported material. The use of heating pins and godets is especially useful for drawing or stretching filaments, threads or yarns composed of a synthetic thermoplastic fiberor film-forming polymer, e.g., polyamides, polyesters, polyolefins and the like. In some cases, it is also desirable to apply a brief heat treatment for the purpose of heat-fixing a texturized yarn or fibrous material, including ribbons, foils, bands or the like. The term filiform is intended to apply herein to all such materials which are commonly transported or conducted in large numbers over identical heating devices in order to impart a uniform heat treatment thereto.

A typical process of this type is described in U. S.

1 such as heated plates, run vertically in the apparatus as Pat. No. 3,441,993. In the apparatus disclosed in this I patent, the individual heating devices or units in the form of hollow heating elements have inlet and outlet means connected to a common supply line for introducing a heated condensing vapor such as saturated steam. A special constriction means is then recommended for arrangement in the supply line in order to provide a reduced flow passage within that portion of the supply line adjacent to each heating element. The constriction means are also operatively associated with the inlet and outlet of each heating element with the intention of uniformly regulating the vapor supply, vapor discharge and condensate discharge in allof the heating elements. In essence, the apparatus of this patent includes special inserts for the supply conduit which exhibit a converging-diverging cross-sectional configura tion, thereby providing a certain suction effect at the outlet of each individual heating element. Thus, a high pressure drop is achieved between the inletand outlet of each hollow heating element, which is supposed to result in not only a more uniform steam supply and discharge but also a more efficient flushing out of the condensate and non-condensing gases such as air. However, in previous apparatus of this type, the condensate is generally removed from the heating elements or the circulating system by the force of gravity. The condensate collects in or along the deepest points of the heating elements or conduits, and the gas or steam vapor phase flows separately from the condensate phase with the movement of both phases together .occurring only on the top surface of the condensate. In other words, the condensate may be moved along the pipes or conduits as a liquid by a certain pumping action of the steam being forced through the same line.

The general arrangement of such a large number of heating units supplied with steam from a common source and adapted to provide a heat treatment of a corresponding plurality of transported filaments, threads, yarns or the like, can be further exemplified as I illustrated in FIGS. I and 6 of US. Pat. No. 3,441,993.

As long as the inlets and outlets to the heating units,

shown in FIG. 1 of the patent, then very little condensate can collect within the heating units and will not cause a variation in the treatment temperature over a period of time by reason of a differing heat transfer coefficient. Nevertheless, it is still quite difficult to adjust each succeeding unit in this apparatus in order to avoid excess accumulation of condensate and variations in the supply of steam through the common feed line, and it is recognized in the patent itself that provision must be made to provide different size inserts or partitions to be interchanged on each heating unit, thereby adapting the apparatus to a wide variety of conditions. The design and installation of such inserts become quite troublesome in practice. On the other hand, if theinlets and outlets of the heating units are arranged horizontally, as shown in FIG. 6 of the cited patent, a portion of the conduit cross-section is always filled with condensate. Where the steam is consumed or condensed in each heating unit, definite temperature differences arise as between the upper portion of the conduit cross-section which is filled with steam moving at one rate nd the lower portion of the conduit crosssection with condensate moving at a different rate. In order to avoid such temperature differences in horizontally arranged heating units or points of steam consumption, it has been previously necessary to use complicated structural changes as shown for example in US. Pat. No. 2,784,410.-Even with the rather complex structure shown in this patent, satisfactory results cannot be obtained if the force of gravity is not sufiicient to counteract the centrifugal force which may be applied by rapidly running godets which are adapted to be heated with steam. In this instance, a condensate film of variable thickness is formed in the godet and this in turn leads to variations in the heat transfer and also in the heat treatment temperature. It will therefore be recognized that prior devices of this type do not necessarily provide a uniform heat-treatment of all of the filaments or thread-like structures in a multi-unit type of device. Moreover, it is also quite difficult to achieve uniform treatment over long periods of continuous operation of such a multi-unit apparatus.

One object of the present invention is to provide an improved method for the uniform heat treatment of a large number of separately transported filaments, threads, yarns, ribbons or the like, i.e., any suitable filiform material, wherein one does not depend upon the force of gravity or complicated structural elements in order to achieve the desired result. Still another object of the invention is to provide such a method as will ensure a substantially complete withdrawal of condensate from individual heating units under all heating conditions or arrangements of the heating devices.

. I 3 It has now been found, in accordance with the invention, that such objects may be achieved in the generally known method described'above using a wide variety of conventional, apparatus, provided that the condensate of the heating vapor is caused to accumulate or collect in the form of very finely divided droplets and to be carried ofi or entrained in this formfrom the heating zone of each individual heating unit, preferably so as to the internal or heated walls of the individual heating zones.

The method of the present invention is thus generally applicable to any conventional method intended forthe uniform heat treatment of a filiform material which is being transported ina plurality of individual paths through corresponding individual heating zones in which surfaces contacting the transported material are indirectly heated by acornmon saturated vapor as a heat exchange fluid, preferably saturated steam. As in conventional methods, this vapor is recirculated to supply the required heat to the internal walls of the heating zones which are arranged in parallel and have substantially identical internal cross-sectional dimensufficiently high to cause substantially all of the condensate the two components of the flowing stream.

Since a saturated vapor such as saturated steam is employed in the method of the invention, the heat supply for each heating unit or heating zone is essentially determined solely on the basis of the amount of con- 7 densation of the saturated vapor. By means of the substantially completely avoid any formation of a condensate film, whether continuous or discontinuous, on

necessary energy, the amount of condensate and therefrom the volumetric ratio of vapor to condensate can beeasily determined; When using thesame-apparatus and method for heat treatment of different filiforrn or filamentary materials, one can also easily determine the precise parameters required to produce I the essential two-phase stream in which fine droplets of the condensate are entrained and withdrawn by the excess vapor. I

Although the essential parameters of the invention which must be maintained above a certain value will vary with any given apparatus or a particular heat exchange fluid, the velocity of the two-phase mixture can be calculated according to the formula:

ar (Q0 Q )/A (meters/second), while the concentration of the gas phase, i.e., the vapor phase in terms of using a saturated vapor, in the entire two-phase mixture can be calculated accordingto the 1 formula:

' -=Q/(Qa+Q1)' (P (2) In these-formulae, Q,(m/sec.) represents the 'volume of the gaseous or vaporousphase in the heating zone,

i.e., the flow volume of the excess vapor amount which must besufiicient to meet all heat requirements as well densate to form a mist of fine dropletsentrained by the 1 flowing vaporwhile also substantially preventing accumulation of any condensate film on the internal walls of the heating zones.

'In the method of the present invention, the condensate isnot led offas a continuous liquid phase separate- 1y from the vapor or gas phase, but instead the condensate is essentially removed by bringing about a twophase stream in which the condensate droplets are mixed with the heating vapor so as to be withdrawn together over the entire conduit cross-section. In order 7 to. bring about such a two-phase stream including fine dropletsof the condensate, it is essential to provide a certain average velocity of the mixture V,,, and also a certain concentration of the gas phase C,, both as more fully defined hereinafter, these values being sufiiciently high at the so-called points ofconsumption," i.e;, in

the heating zones or wherever the steam is caused to condense, such that a condensate film can be substantially prevented on the internal .walls of the heating units or conduits.

In order to determine these particular operating conditions or parameters, one can refer for example'to the as for transportingthe condensate throughout the system. Q1(-rn /sec.) represents the volume of the fluid 3 phase, i.e., the volume of the entrained condensate. Finally, A(m 'is the cross-sectional area in the heating zones or at the points of vapor consumptionflhese formulae can be employed to determine the requirements of each individual heating unit, i.e., within each individual zone, and since all are preferably identical to each other, the total number can be multiplied in order to, detemiine the total amount of excess saturated vapor which must be applied to the system and recirculated therethrough. Also, only a few preliminary experiments are required to determine the minimum I values of V,,, and C, which are required tomaintain the experimental work carried out by C. I. l-loogendoom as described in the article Gas-liquid Flow in Horizontal Pipes, Chemical Engineering Science, 1959, Vol. 9,

pp. 205 to 217, for example where one is working with saturated steam as the gas phase and the condensate as the liquid droplets or finely divided phase. By following readily determine how toachieve the two-phase stream containing the very finely divided condensate droplets based upon a predetermined cross-sectional area of the conduit and a given volumetric ratio of vapor and convtheprinciples of this article, one skilled in this art can essential two-phase vapor/condensate stream flowing through each heating unit or heating zone.

When working with saturated steam, which is most economical and expedient as the heat exchange fluid, one can be certain to achieve the withdrawal of the condensate from the heating elements in the form of very finely divided droplets if the average velocity of the two-phase mixture V,,, is maintained at the points of steam consumption at a value greater than 8 meters/second, while the gas or vapor concentration C, is

also maintained at a value greater than 97 percent. When using a heat exchange medium other than saturated steam, it will of coursebe necessary to establish other minimum values in the manner'outlined above. Moreover, once these minimum values are determined, a basis is provided for designing the heating units and the supply of steam or other heating vapor in such a manner as to achieve the best possible results.

The recirculation of the heating ,vapor is advantageously achieved in the method of the invention by means of a jet pump, sometimes referred to more simply as an injector, whereby in addition to the recirculation one also achieves at the same time the required compression to a higher pressure or higher energy level. The jet compressor or injector pump thus serves to supply the heating vapor at a high pressure on the inlet side of theheating units while also maintaining the desired high streamvelocity in each of these heating units. The injected or propellant steam for this jet pump can be supplied from a central main or it can also be fed from a separate steam boiler or generator.

The jet compresser or injector pump is preferably dimensioned in such a manner that the freshly injected amounts of propellant vapor are approximately equal to the amount of vapor being condensed in the heating system. Also, the pressure of the fresh or injected vapor, i.e., the so-called booster pressure, is thus greater than the saturated vapor pressure of the heating zones, this booster pressure being determined essentially by the desired velocity of the two-phase vapor/condensate mixture.

In comparison to known heating systems of this type, the use of a jet compresser or injector pump for purposes of the present invention results in an energy saving of about 30 percent.

It is preferable of course to conduct the individual streams of saturated vapor with the entrained condensate droplets as they issue from the individual heating zones into a common pipe or manifold and to include a steam generator or boiler in the recycle stream.

In this case, the finely divided droplets of the condensate can be separated in an advantageous manner by passing the common stream of vapors obtained from the individual heating zones into a conventional condensate separator. The condensate separated at this point can be conducted from the separator into a separate boiler or else it can also be fed over an expansion zone or pressure releasing device into a vapor line or system maintained at lower pressure level. The gas or vapor freed of the condensate can finally again be compressed while preferably at the same time introducing an amount of saturated vapor corresponding to the separated and withdrawn condensate.

The method of the invention is more fully explained in detail by the following example taken together with the accompanying drawing in which the single FIGURE is a schematic flow sheet representation of suitable apparatus for the heating system. In particular, this drawing illustrates only the recirculation of the saturated vapor through a large number of heating units or heating zones, the remaining textile apparatus or other means for transporting a corresponding number of individual filaments, threads, ribbons or the like being omitted since any conventional means can be used for transporting, drawing or stretching such filiform materials. It will be understood that the invention is not restricted to this specific example.

EXAMPLE Along a thread drawing apparatus provided with means for drawing 24 threads, each having a yarn size of 1000 dtex, there are provided between a feed distributor line 1 and a collection line 2, a complete series of individual vapor lines 3 containing individual heating units or heating zones 4 which correspond in number to I returning the vapor through line 8 to the injector 6.

Through the make-up or fresh feed line 9, there are introduced 16 kilograms per hour of fresh steam. This fresh steam serves as a propellant for compressing the gaseous or vaporous steam as it is recycled through line 8 into the injector 6. The pressure of this fresh steam at 9 amounts to 7.1 atmospheres (absolute) at a temperature of 165C. In the entire recirculation system, approximately 1 l 1 kilograms per hour of steam are recirculated. At the same time, 16 kilograms of condensate are separated and withdrawn through line 10 by means of pump 11. Thus, this amount of withdrawn condensate corresponds to the amount of fresh steam introduced through line 9. The condensate exiting from pump 1 1 can be returned to a steam boiler or expanded into steam lines maintained at lower pressures.

The released heat of condensation is sufficient to bring about a heating up of the threads from 80 C. to about 145 C. as these threads run at a speed of about 250 meters/minute over the heating tubes 4. At a saturated steam temperature of 150 C., a pressure of 4.854 atmospheres (absolute) prevails in the heating system, i.e., at the point of consumption in the tubular heaters The injector 6 is constructed as a jet compresser or propellant nozzle, the propellant gas being injected at a velocity of 381 meters/second so as to achieve a velocity of the mixed vapors of 134.5'meters/second. In otherwords, the recycled vapor through line 8 is mixed with the propellant fresh steam 9 in the injector 6 so as to achieve the latter velocity.

Under the conditions mentioned above, a coherent stream is established in which the condensate is formed substantially only as very finely divided droplets and transported off by the excess amounts of steam. The individual heating elements or zones thereby remain substantially free of condensate, i.e., so that no condensate film runs along the interior walls of these heating zones. As a result, the temperatures can be maintained substantially constant over all of the 24 heating zones.

From the foregoing information, one can easily calculate the average velocity of the two-phase mixture V which is equal to 8.36 meters/second. This is essentially determined from the amount of condensate Q 16 kg/hr and an amount of excess saturated steam Q, Ill 116 kg/hr, with a specific volume of the condensate of V 0.00109 m /kg as well as a specific volume of the steam of V" 0.3824 m lkg. Correspondingly, from the above noted equations, one can also calculate the concentration of the steam or gas phase C, 99.95 percent.

In the foregoing example, all pressures are measured in atmospheres (absolute) on the basis that 1 atm. l

kglcm i.e., corresponding to 14.2233 psi. Also, saturated steam is employed as the heating vapor because of its economy and availability, saturated steam representing the so called gas phase as from the liquid phase formed by the condensate.

In this respect, it should be noted that in the method of the invention, the formation and discharge of the condensate as very finely divided droplets shouldoccur with substantially all of the condensate being formed in i the heating zones, or steam consumption points, i.e.,

ous layer or even as a collection of droplets on the walls of the heating zones. This prevention of a continuous film or condensate layer and preferably even a discon- 3 such that the condensate does not deposit as a continu- I tinuous layer is extremely important in achieving highly uniform temperature conditions at each heating position and likewise as between all heating positions. Furthermore, the omission of a-conden'sate film substantially improves the heat transfer of each. heating unit.

. The formation of the condensate as fine to very fine droplets capable of being entrained and withdrawn by the excess saturated vapor occurs only under the criti-' 'cal conditions outlined hereinabove, and the resulting fog or mist of the condensate remains very uniformly mixed with'the saturated vapor over the cross-section of the heating zones or subsequent conduits untilseparated during recirculation. The energy losses in-, curredaresurprisingly quite low.

Themethod r the invention can be used in .n instancesin which one or especially many separately transported linear or extended textile structures must The invention is hereby claimed as follows: 1. in a method for the uniform heat treatment of a filifonn material being transported in a plurality of in- .dividual paths through corresponding individual heat- 7 ing zones in which surfaces contacting the transported material are indirectly heated by a common saturated vapor as a heat exchange fluid, said vapor being recirculated to supply the required heat to the internal walls of said heating zones which are arranged in parallel and have substantially identical internal cross-sectional dimensions with reference to fluid flow therethrough, the improvement which comprises carrying off the condensate portion of the vapor accumulating in each of said heating zones by supplying excess saturated vapor to each said zone at an average flow velocity V, and a concentration .of the gas phase C, whichare both sufficiently high to cause substantially all of the condensate to form a mist of fine droplets entrained by the flowing be thermally treated under especially uniform eonditions. The method is applicable to horizontally as well as vertically installed heating plates, tubes, pins or the like and leads to especially favorable and improved results when working with rotating heated godets or drums. Although the method is primarily intended to like, it can also be used to advantage for the treatment of cheaper plastic wires, monofilaments or cables.

vapor while also substantially preventing accumulation of any condensate film on the internal walls of the heating zones.

2. A method as claimed in claim 1 wherein the saturated vapor is saturated steam. a

3. A method as claimed in claim 2 wherein the aver ters/ rated vapor is recirculated by means of a jet pump which also supplies fresh vapor as the propellant.

6. A method as claimed in claim 5 wherein the amount of fresh vapor being supplied by said jet pump as the propellant is approximately equal to the amount be used with textile products consisting of linear fiberor film-fonning polymers, e.g., polyesters, nylons or the of vapor being condensed in all of the heating zones.

7. A method as claimed in claim 6 wherein the saturated vapor is saturated steam.

. r a: a: a:

l V th 8 or i a nd tfi gb iicen eiieriili tlf esginse Elie greater than 97 percent in each of said heating zones.

gggy UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5,6 2, 38 Dated August 8, 1972 Inventor(s) OBterta-S 9t -1 It is certified that error appears in the abve-identified patent and that said Letters Patent are hereby corrected as shown below:

Coverpage, left hand column, insert 73 Assignee:

A-kzona Incorporated,

NICO

Signed and sealed this 13th day of February 1973.

(SEAL) Attest:

EDWARD M.I LETCI-'IER,JR. ROBERT GOTTSCHALK Attesting Officer 7 Commissioner of Patents 

1. In a method for the uniform heat treatment of a filiform material being transported in a plurality of individual paths through corresponding individual heating zones in which surfaces contacting the transported material are indirectly heated by a common saturated vapor as a heat exchange fluid, said vapor being recirculated to supply the required heat to the internal walls of said heating zones which are arranged in parallel and have substantially identical internal cross-sectional dimensions with reference to fluid flow therethrough, the improvement which comprises carrying off the condensate portion of the vapor accumulating in each of said heating zones by supplying excess saturated vapor to each said zone at an average flow velocity Vm and a concentration of the gas phase Cg which are both sufficiently high to cause substantially all of the condensate to form a mist of fine droplets entrained by the flowing vapor while also substantially preventing accumulation of any condensate film on the internal walls of the heating zones.
 2. A method as claimed in claim 1 wherein the saturated vapor is saturated steam.
 3. A method as claimed in claim 2 wherein the average flow velocity Vm is greater than 8 meters/second and the concentration of the gas phase Cg is greater than 97 percent in each of said heating zones.
 4. A method as claimed in claim 1 wherein the saturated vapor containing the entrained droplets from each heating zone are collected and passed in common through a condensate separator.
 5. A method as claimed in claim 1 wherein the saturated vapor is recirculated by means of a jet pump which also supplies fresh vapor as the propellant.
 6. A method as claimed in claim 5 wherein the amount of fresh vapor being supplied by said jet pump as the propellant is approximately equal to the amount of vapor being condensed in all of the heating zones.
 7. A method as claimed in claim 6 wherein the saturated vapor is saturated steam. 